The present invention relates generally to the controlling of movement of an implement, and more specifically, for controlling the velocity of an implement.
Many conventional control systems use position control to control the movement of an implement. Thus, for a given input signal, the control system will move the implement to a discrete position, i.e., a 1:1 correspondence exists between the input and the position of the implement. Many input devices, such as joysticks, however, are used to provide relative movement commands. For example, deflecting a joystick 20 degrees to the left may indicate a desire to move the implement to the left a rate of 1 cm per second, while deflecting the joystick 40 degrees to the left indicates a desire to move the implement to the left at a rate of 5 cm per second. Thus, the input device provides a velocity, rather than position signal. In order to use this signal with position control, the velocity is integrated, providing a position signal that is input to the control system.
The use of integrators however, introduces several problems. For example, an operator may desire to move the arm of a hitch slightly to the left. Thus, the operator deflects the joystick slightly to the left. If the arm is physically prevented from moving, such as by an excessive load opposing the motion, the operator may continue to hold the joystick in the deflected position until seeing movement by the arm (e.g., after the load is removed). While the joystick is held in a deflected position, the integrator continues to integrate the commanded velocity. When the arm finally moves, the (position) output from the integrator may be large in magnitude, commanding the arm to move to a position much further to the left than intended by the operator (because the desired position is proportional to the magnitude of the output of the integrator). In addition, the integrator requires additional circuitry, increasing the complexity of the system and reducing its reliability.
Conventional control systems also typically respectively compare a single desired position or velocity with the actual position or velocity, producing an error signal corresponding to the difference. Thus, any adjustment to either the desired position signal or actual position signal affects the error signal, thereby affecting the entire control system. Thus the control system has uniform characteristics throughout, and the conventional control system cannot vary its performance, such as being more or less responsive to the input when the implement being controlled is in a predetermined position.
The present invention provides apparatus and methods for determining a velocity of an implement. A first processing device receives a first arm limit position signal and a first arm actual position signal. The first processing device determines a difference between the first arm limit position signal and the first arm actual position signal, and transmits a first arm position error signal as a function of the difference. A second processing device receives the first arm position error signal transmits a first arm velocity signal as a function of the first arm position error signal multiplied by a first predetermined function. A third processing device receives a first arm desired position signal and the first arm actual position signal. The third processing device determines a difference between the first arm desired position signal and the first arm actual position signal, and transmits a second position error signal as a function of the difference. A fourth processing device receives the second position error signal and transmit a second velocity signal as a function of the second position error signal multiplied by a second predetermined function. A fifth processing device receives the first arm velocity signal and the second velocity signal. The fourth processing device transmits a desired velocity signal as a function of the first arm velocity signal when the first arm velocity signal has a predetermined relationship to the second velocity signal, and transmits a desired velocity signal as a function of the second velocity signal when the first arm velocity signal does not have the predetermined relationship to the second velocity signal.